Sinter powder containing a mineral flame retardant for producing moulded bodies

ABSTRACT

The present invention relates to a process for producing a shaped body, wherein, in step i), a layer of a sinter powder (SP) comprising at least one mineral flame retardant inter alia is provided and, in step ii), the layer provided in step i) is exposed. The present invention further relates to a process for producing a sinter powder (SP) and to a sinter powder (SP) obtainable by this process. The present invention also relates to the use of the sinter powder (SP) in a sintering process and to shaped bodies obtainable by the process of the invention.

The present invention relates to a process for producing a shaped body,wherein, in step i), a layer of a sinter powder (SP) comprising at leastone mineral flame retardant inter alia is provided and, in step ii), thelayer provided in step i) is exposed. The present invention furtherrelates to a process for producing a sinter powder (SP) and to a sinterpowder (SP) obtainable by this process. The present invention alsorelates to the use of the sinter powder (SP) in a sintering process andto shaped bodies obtainable by the process of the invention.

The rapid provision of prototypes is a problem often addressed in veryrecent times. One process which is particularly suitable for thisso-called “rapid prototyping” is selective laser sintering (SLS). Thisinvolves selectively irradiating a plastic powder in a chamber with alaser beam. The powder melts, the molten particles coalesce andresolidify. Repeated application of plastic powder and subsequentirradiation with a laser allows modeling of three-dimensional shapedbodies.

The process of selective laser sintering for producing shaped bodiesfrom pulverulent polymers is described in detail in patentspecifications U.S. Pat. No. 6,136,948 and WO 96/06881.

Selective laser sintering is frequently too time-consuming for theproduction of a relatively large number of shaped bodies, and so it ispossible to produce relatively large volumes of shaped bodies usinghigh-speed sintering (HSS) or “multijet fusion technology” (MJF) fromHP. In high-speed sintering, by spray application of aninfrared-absorbing ink onto the component cross section to be sintered,followed by exposure with an infrared source, a higher processing speedis achieved compared to selective laser sintering.

However, a disadvantage of high-speed sintering is that the powdershould not sinter outside the shaped body cross section to be sintered,nor should it stick together. Therefore, it is necessary to use as low aconstruction space temperature as possible in the production. The effectof this is frequently that the melting of the shaped body is not good inthe shaped body cross section to be sintered and/or resultant highcomponent warpage.

There is also frequently component warpage in selective laser sintering.If further components (e.g. flame retardant) are present in the sinterpowder as well as a pure polyamide or another pure semicrystallinepolymer, the sintering window of the sinter powder is frequently reducedin the selective laser sintering operation. A reduction in the sinteringwindow frequently leads to warpage of the shaped bodies during theproduction by selective laser sintering. This warpage virtually rulesout use or further processing of the shaped bodies. Even during theproduction of the shaped bodies, the warpage can be so severe thatfurther layer application is impossible and therefore the productionprocess has to be stopped.

A problem both with high-speed sintering or multi-jet fusion technologyand with selective laser sintering is additionally that the resultantshaped bodies frequently have low heat distortion resistance andfrequently fail flame retardancy tests. The effect of the addition offlame retardants to improve fire resistance is frequently that thecomponents present in the sinter powder react with the flame retardant,for example in the form of crosslinking reactions, and hence have alasting adverse effect on the properties thereof. Moreover, it isproblematic that flame retardants frequently lead to unwanted or eventoxic emissions in the construction space when the sinter powders areused in the methods mentioned.

It was thus an object of the present invention to provide a process forproducing shaped bodies which has the aforementioned disadvantages ofthe processes described in the prior art only to a reduced degree, if atall. The process should additionally be performable in a simple andinexpensive manner.

This object is achieved by a process for producing a shaped body,comprising the steps of

i) providing a layer of a sinter powder (SP) comprising the followingcomponents:

-   -   (A) at least one semicrystalline polyamide,    -   (B) at least one amorphous polyamide,    -   (C) at least one mineral flame retardant,

ii) exposing the layer of the sinter powder (SP) provided in step i).

It has been found that, surprisingly, shaped bodies that have beenproduced by the process of the invention have a particularly good UL 94flame retardancy level without any adverse effect on the otherproperties of the shaped bodies. Surprisingly, there is even improvementin some properties of the shaped bodies. More particularly, the shapedbodies produced by the process of the invention still have particularlygood mechanical properties, especially a high modulus and good tensilestrength, and elevated toughness relative to shaped bodies that do notcomprise any component (C). The shaped bodies produced in accordancewith the invention additionally have particularly good heat distortionresistance.

The sinter powder of the invention additionally has good thermooxidativestability, which results in good reusability of the sinter powder (SP),i.e. good recyclability from the construction space.

More particularly, the process of the invention is also of goodsuitability as a selective laser sintering process and as a high-speedsintering process or multijet fusion process since the sinter powder(SP) used in accordance with the invention has a broad sintering window.

The process of the invention is elucidated in detail hereinafter.

Step i)

In step i), a layer of the sinter powder (SP) is provided.

The layer of the sinter powder (SP) can be provided by any methods knownto those skilled in the art. Typically, the layer of the sinter powder(SP) is provided in a construction space on a construction platform. Thetemperature of the construction space may optionally be controlled.

The construction space has, for example, a temperature in the range from1 to 100 K (kelvin) below the melting temperature (T_(M)) of the sinterpowder (SP), preferably a temperature in the range from 5 to 50 K belowthe melting temperature (T_(M)) of the sinter powder (SP) and especiallypreferably a temperature in the range from 10 to 25 K below the meltingtemperature (T_(M)) of the sinter powder (SP).

The construction space has, for example, a temperature in the range from150 to 250° C., preferably in the range from 160 to 230° C. andespecially preferably in the range from 170 to 210° C.

The layer of the sinter powder (SP) can be provided by any methods knownto those skilled in the art. For example, the layer of the sinter powder(SP) is provided by means of a coating bar or a roll in the thickness tobe achieved in the construction space.

The thickness of the layer of the sinter powder (SP) which is providedin step i) may be as desired. For example, it is in the range from 50 to300 μm, preferably in the range from 70 to 200 μm and especiallypreferably in the range from 90 to 150 μm.

Sinter Powder (SP)

According to the invention, the sinter powder (SP) comprises at leastone semicrystalline polyamide as component (A), at least one amorphouspolyamide as component (B), and at least one mineral flame retardant ascomponent (C).

In the context of the present invention the terms “component (A)” and“at least one semicrystalline polyamide” are used synonymously andtherefore have the same meaning.

The same applies to the terms “component (B)” and “at least oneamorphous polyamide”. These terms are likewise used synonymously in thecontext of the present invention and therefore have the same meaning.

Correspondingly, the terms “component (C)” and “at least one mineralflame retardant” are also used synonymously in the context of thepresent invention and have the same meaning.

The sinter powder (SP) may comprise components (A), (B) and (C) in anydesired amounts.

For example, the sinter powder (SP) comprises in the range from 30% to70% by weight of component (A), in the range from 5% to 25% by weight ofcomponent (B) and in the range from 20% to 60% by weight of component(C), based in each case on the sum total of the percentages by weight ofcomponents (A), (B) and (C), preferably based on the total weight of thesinter powder (SP).

Preferably, the sinter powder (SP) comprises in the range from 40% to70% by weight of component (A), in the range from 7% to 23% by weight ofcomponent (B) and in the range from 22% to 45% by weight of component(C), based in each case on the sum total of the percentages by weight ofcomponents (A), (B) and (C), preferably based on the total weight of thesinter powder (SP).

Most preferably, the sinter powder (SP) comprises in the range from 50%to 65% by weight of component (A), in the range from 10% to 20% byweight of component (B) and in the range from 25% to 35% by weight ofcomponent (C), based in each case on the sum total of the percentages byweight of components (A), (B) and (C), preferably based on the totalweight of the sinter powder (SP).

The present invention therefore also provides a process in which thesinter powder (SP) comprises in the range from 30% to 70% by weight ofcomponent (A), in the range from 5% to 25% by weight of component (B)and in the range from 20% to 60% by weight of component (C), based ineach case on the total weight of the sinter powder (SP).

The sinter powder (SP) may further comprise at least one additive. Forexample, the at least one additive is selected from the group consistingof antinucleating agents, stabilizers, flow aids, end groupfunctionalizers, dyes and color pigments.

An example of a suitable antinucleating agent is lithium chloride.Suitable stabilizers are, for example, phenols, phosphites and copperstabilizers.

Suitable end group functionalizers are, for example, terephthalic acid,adipic acid and propionic acid. Suitable dyes and color pigments are,for example, carbon black and iron chromium oxides.

Suitable flow aids are, for example, silicas or aluminas. A preferredflow aid is alumina. An example of a suitable alumina is Aeroxide® Alu Cfrom Evonik.

For example, the sinter powder (SP) comprises in the range from 0.1% to10% by weight of the at least one additive, preferably in the range from0.2% to 5% by weight and especially preferably in the range from 0.3% to2.5% by weight, based in each case on the total weight of the sinterpowder (SP).

The present invention therefore also provides a process in which thesinter powder (SP) additionally comprises in the range from 0.1% to 10%by weight of at least one additive selected from the group consisting ofantinucleating agents, stabilizers, end group functionalizers, dyes andcolor pigments, based on the total weight of the sinter powder (SP).

Preferably, the sinter powder (SP) also additionally comprises at leastone reinforcing agent.

For example, the sinter powder (SP) comprises in the range from 5% to60% by weight, preferably in the range from 10% to 50% by weight andespecially preferably in the range from 15% to 40% by weight of at leastone reinforcing agent, based in each case on the total weight of thesinter powder (SP).

The percentages by weight of components (A), (B) and (C) and optionallyof the at least one additive and the at least one reinforcing agenttypically add up to 100% by weight.

In the context of the present invention, “at least one reinforcingagent” means either exactly one reinforcing agent or a mixture of two ormore reinforcing agents.

In the context of the present invention, a reinforcing agent isunderstood to mean a material that improves the mechanical properties ofshaped bodies produced by the process of the invention compared toshaped bodies that do not comprise the reinforcing agent.

Reinforcing agents as such are known to those skilled in the art. Forexample, the at least one reinforcing agent may be in spherical form, inplatelet form or in fibrous form.

Preferably, the at least one reinforcing agent is in platelet form or infibrous form.

A “fibrous reinforcing agent” is understood to mean a reinforcing agentin which the ratio of length of the fibrous reinforcing agent to thediameter of the fibrous reinforcing agent is in the range from 2:1 to40:1, preferably in the range from 3:1 to 30:1 and especially preferablyin the range from 5:1 to 20:1, where the length of the fibrousreinforcing agent and the diameter of the fibrous reinforcing agent aredetermined by microscopy by means of image evaluation on samples afterashing, with evaluation of at least 70 000 parts of the fibrousreinforcing agent after ashing.

The length of the fibrous reinforcing agent in that case is typically inthe range from 5 to 1000 am, preferably in the range from 10 to 600 μmand especially preferably in the range from 20 to 500 μm, determined bymeans of microscopy with image evaluation after ashing.

The diameter in that case is, for example, in the range from 1 to 30 μm,preferably in the range from 2 to 20 μm and especially preferably in therange from 5 to 15 μm, determined by means of microscopy with imageevaluation after ashing.

In a further preferred embodiment, the at least one reinforcing agent isin platelet form. In the context of the present invention, “in plateletform” is understood to mean that the particles of the at least onereinforcing agent have a ratio of diameter to thickness in the rangefrom 4:1 to 10:1, determined by means of microscopy with imageevaluation after ashing.

Suitable reinforcing agents are known to those skilled in the art andare selected, for example, from the group consisting of carbonnanotubes, carbon fibers, boron fibers, glass fibers, glass beads,silica fibers, ceramic fibers, basalt fibers, aluminosilicates, aramidfibers and polyester fibers.

Preferred fibrous reinforcing agents are glass fibers and/or carbonfibers. These reinforcing agents may additionally have beenaminosilane-functionalized.

Suitable silica fibers are, for example, wollastonite.

Suitable aluminosilicates are known as such to the person skilled in theart. Aluminosilicates refer to compounds comprising Al₂O₃ and SiO₂. Instructural terms, a common factor among the aluminosilicates is that thesilicon atoms are tetrahedrally coordinated by oxygen atoms and thealuminum atoms are octahedrally coordinated by oxygen atoms.Aluminosilicates may additionally comprise further elements.

Preferred aluminosilicates are sheet silicates. Particularly preferredaluminosilicates are calcined aluminosilicates, especially preferablycalcined sheet silicates. The aluminosilicate may additionally have beenaminosilane-functionalized.

If the at least one reinforcing agent is an aluminosilicate, thealuminosilicate may be used in any form. For example, it can be used inthe form of the pure aluminosilicate, but it is likewise possible thatthe aluminosilicate is used in mineral form. Preferably, thealuminosilicate is used in mineral form. Suitable aluminosilicates are,for example, feldspars, zeolites, sodalite, sillimanite, andalusite andkaolin. Kaolin is a preferred aluminosilicate.

The present invention therefore also provides a process in which thesinter powder (SP) additionally comprises kaolin as at least onereinforcing agent.

Kaolin is one of the clay rocks and comprises essentially the mineralkaolinite. The empirical formula of kaolinite is Al₂[(OH)₄/Si₂O₅].Kaolinite is a sheet silicate. As well as kaolinite, kaolin typicallyalso comprises further compounds, for example titanium dioxide, sodiumoxides and iron oxides. Kaolin preferred in accordance with theinvention comprises at least 98% by weight of kaolinite, based on thetotal weight of the kaolin.

The sinter powder (SP) comprises particles. These particles have, forexample, a size in the range from 10 to 250 μm, preferably in the rangefrom 15 to 200 μm, more preferably in the range from 20 to 120 μm andespecially preferably in the range from 20 to 110 μm.

The sinter powder (SP) of the invention has, for example,

a D10 in the range from 10 to 60 μm,

a D50 in the range from 25 to 90 μm and

a D90 in the range from 50 to 150 am.

Preferably, the sinter powder (SP) of the invention has

a D10 in the range from 20 to 50 μm,

a D50 in the range from 40 to 80 μm and

a D90 in the range from 80 to 125 am.

The present invention therefore also provides a process in which thesinter powder (SP) has

a D10 in the range from 10 to 60 μm,

a D50 in the range from 25 to 90 μm and

a D90 in the range from 50 to 150 μm.

In the context of the present invention, the “D10” is understood to meanthe particle size at which 10% by volume of the particles based on thetotal volume of the particles are smaller than or equal to D10 and 90%by volume of the particles based on the total volume of the particlesare larger than D10. By analogy, the “D50” is understood to mean theparticle size at which 50% by volume of the particles based on the totalvolume of the particles are smaller than or equal to D50 and 50% byvolume of the particles based on the total volume of the particles arelarger than D50. Correspondingly, the “D90” is understood to mean theparticle size at which 90% by volume of the particles based on the totalvolume of the particles are smaller than or equal to D90 and 10% byvolume of the particles based on the total volume of the particles arelarger than D90.

To determine the particle sizes, the sinter powder (SP) is suspended ina dry state using compressed air or in a solvent, for example water orethanol, and this suspension is analyzed. The D10, D50 and D90 valuesare determined by laser diffraction using a Malvern Mastersizer 3000.Evaluation is by means of Fraunhofer diffraction.

The sinter powder (SP) typically has a melting temperature (T_(M)) inthe range from 160 to 280° C. Preferably, the melting temperature(T_(M)) of the sinter powder (SP) is in the range from 170 to 265° C.and especially preferably in the range from 175 to 245° C.

The melting temperature (T_(M)) is determined in the context of thepresent invention by means of differential scanning calorimetry (DSC).Typically, a heating run (H) and a cooling run (K) are measured, each ata heating rate/cooling rate of 20 K/min. This affords a DSC diagram asshown by way of example in FIG. 1. The melting temperature (T_(M)) isthen understood to mean the temperature at which the melting peak of theheating run (H) of the DSC diagram has a maximum.

The sinter powder (SP) typically also has a crystallization temperature(T_(C)) in the range from 120 to 250° C. Preferably, the crystallizationtemperature (T_(C)) of the sinter powder (SP) is in the range from 130to 240° C. and especially preferably in the range from 140 to 235° C.

The present invention therefore also provides a process in which thesinter powder (SP) has a crystallization temperature (T_(C)) in therange from 120 to 250° C.

The crystallization temperature (T_(C)) is determined in the context ofthe present invention by means of differential scanning calorimetry(DSC). This typically involves measuring a heating run (H) and a coolingrun (K), each at a heating rate and a cooling rate of 20 K/min. Thisaffords a DSC diagram as shown by way of example in FIG. 1.

The crystallization temperature (T_(C)) is then the temperature at theminimum of the crystallization peak of the DSC curve.

The sinter powder (SP) typically also has a sintering window (W_(SP)).The sintering window (W_(SP)) is, as described below, the differencebetween the onset temperature of melting (T_(M) ^(onset)) and the onsettemperature of crystallization (T_(C) ^(onset)). The onset temperatureof melting (T_(M) ^(onset)) and the onset temperature of crystallization(T_(C) ^(onset)) are determined as described below.

The sintering window (W_(SP)) of the sinter powder (SP) is, for example,in the range from 10 to 40 K (kelvin), more preferably in the range from15 to 35 K and especially preferably in the range from 18 to 30 K.

The sinter powder (SP) can be produced by any methods known to thoseskilled in the art. For example, components (A), (B) and (C) andoptionally the at least one additive and the at least one reinforcingagent may be ground with one another.

The grinding can be conducted by any methods known to those skilled inthe art; for example, components (A), (B) and (C) and optionally the atleast one additive and the at least one reinforcing agent are introducedinto a mill and ground therein.

Suitable mills include all mills known to those skilled in the art, forexample classifier mills, opposed jet mills, hammer mills, ball mills,vibratory mills or rotor mills.

The grinding in the mill can likewise be effected by any methods knownto those skilled in the art. For example, the grinding can take placeunder inert gas and/or while cooling with liquid nitrogen. Cooling withliquid nitrogen is preferred. The temperature in the grinding is asdesired; preference is given to conducting the grinding at temperaturesof liquid nitrogen, for example at a temperature in the range from −210to −195° C. The temperature of the components during the grinding inthat case is, for example, in the range from −40 to −30° C.

Preferably, the components are first mixed with one another and thenground. The process for producing the sinter powder (SP) in that casepreferably comprises the steps of

a) mixing the following components:

-   -   (A) at least one semicrystalline polyamide,    -   (B) at least one amorphous polyamide,    -   (C) at least one mineral flame retardant,

b) grinding the mixture obtained in step a) to obtain the sinter powder(SP).

The present invention therefore also provides a process for producing asinter powder (SP), comprising the steps of

a) mixing the following components:

-   -   (A) at least one semicrystalline polyamide,    -   (B) at least one amorphous polyamide,    -   (C) at least one mineral flame retardant,

b) grinding the mixture obtained in step a) to obtain the sinter powder(SP).

In a preferred embodiment, the process for producing the sinter powder(SP) comprises the following steps:

-   ai) mixing the following components:    -   (A) at least one semicrystalline polyamide,    -   (B) at least one amorphous polyamide,    -   (C) at least one mineral flame retardant,-   bi) grinding the mixture obtained in step ai) to obtain a polyamide    powder,-   bii) mixing the polyamide powder obtained in step bi) with a flow    aid to obtain the sinter powder (SP).

Suitable flow aids are, for example, silicas or aluminas. A preferredflow aid is alumina. An example of a suitable alumina is Aeroxide® Alu Cfrom Evonik.

If the sinter powder (SP) comprises a flow aid, it is preferably addedin process step bii). In one embodiment, the sinter powder (SP)comprises 0.1% to 1% by weight, preferably 0.2% to 0.8% by weight andmore preferably 0.3% to 0.6% by weight of flow aid, based in each caseon the total weight of the sinter powder (SP) and the flow aid.

The present invention therefore also further provides a process in whichstep b) comprises the following steps:

-   bi) grinding the mixture obtained in step a) to obtain a polyamide    powder,-   bii) mixing the polyamide powder obtained in step bi) with a flow    aid to obtain the sinter powder (SP).

Processes for compounding (for mixing) in step a) are known as such tothose skilled in the art. For example, the mixing can be effected in anextruder, especially preferably in a twin-screw extruder.

The present invention therefore also provides a process for producing asinter powder (SP), in which the components are mixed in step a) in atwin-screw extruder.

In respect of the grinding in step b), the details and preferencesdescribed above are correspondingly applicable with regard to thegrinding.

The present invention therefore also further provides the sinter powder(SP) obtainable by the process of the invention.

In one embodiment of the present invention, component (C) in the sinterpowder (SP) has been coated with component (A) and/or with component(B).

Component (C) has been coated with component (A) and/or component (B)especially when the sinter powder (SP) has been produced by first mixing(compounding) components (A), (B) and (C) with one another, preferablywhen the sinter powder (SP) is produced by the above-described processcomprising steps a) and b).

The present invention therefore also provides a process in whichcomponent (C) in the sinter powder (SP) has been coated with component(A) and/or with component (B).

In a further embodiment of the present invention, the sinter powder (SP)is in the form of a mixture. In other words, in this embodiment,components (A), (B) and (C) are present alongside one another andcomponent (C) has not been coated with component (A) and/or component(B).

It will be appreciated that it is also possible for one portion ofcomponent (C) to have been coated with component (A) and/or component(B) and another portion of component (C) not to have been coated withcomponent (A) and/or component (B).

Component (A)

According to the invention, component (A) is at least onesemicrystalline polyamide.

In the context of the present invention “at least one semicrystallinepolyamide” means either exactly one semicrystalline polyamide or amixture of two or more semicrystalline polyamides.

“Semicrystalline” in the context of the present invention means that thepolyamide has an enthalpy of fusion ΔH2_((A)) of greater than 45 J/g,preferably of greater than 50 J/g and especially preferably of greaterthan 55 J/g, in each case measured by means of differential scanningcalorimetry (DSC) according to ISO 11357-4:2014.

The at least one semicrystalline polyamide (A) of the invention thustypically has an enthalpy of fusion ΔH2_((A)) of greater than 45 J/g,preferably of greater than 50 J/g and especially preferably of greaterthan 55 J/g, in each case measured by means of differential scanningcalorimetry (DSC) according to ISO 11357-4:2014.

The at least one semicrystalline polyamide (A) of the inventiontypically has an enthalpy of fusion ΔH2_((A)) of less than 200 J/g,preferably of less than 150 J/g and especially preferably of less than100 J/g, in each case measured by means of differential scanningcalorimetry (DSC) according to ISO 11357-4:2014.

Suitable semicrystalline polyamides (A) generally have a viscositynumber (VN_((A))) in the range from 90 to 350 mL/g, preferably in therange from 100 to 275 mL/g and especially preferably in the range from110 to 250 mL/g, determined in a 0.5% by weight solution of 96% byweight sulfuric acid at 25° C., measured to ISO 307:2013-8.

The present invention thus also provides a process in which component(A) has a viscosity number (VN_((A))) in the range from 90 to 350 mL/g,determined in a 0.5% by weight solution of component (A) in 96% byweight sulfuric acid at 25° C.

Component (A) of the invention typically has a melting temperature(T_(M(A))). Preferably, the melting temperature (T_(M(A))) of component(A) is in the range from 170 to 280° C., more preferably in the rangefrom 180 to 265° C. and especially preferably in the range from 185 to245° C., determined to ISO 11357-3:2014.

The present invention thus also provides a process in which component(A) has a melting temperature (T_(M(A))), where the melting temperature(T_(M(A))) is in the range from 170 to 230° C.

Suitable components (A) have a weight-average molecular weight(M_(W(A))) in the range from 500 to 2 000 000 g/mol, preferably in therange from 10 000 to 90 000 g/mol and especially preferably in the rangefrom 20 000 to 70 000 g/mol. The weight-average molecular weight(M_(W(A))) is determined by means of SEC-MALLS (Size ExclusionChromatography-Multi-Angle Laser Light Scattering) according to Chi-sanWu “Handbook of size exclusion chromatography and related techniques”,page 19.

Suitable as the at least one semicrystalline polyamide (A) are, forexample, semicrystalline polyamides (A) that derive from lactams having4 to 12 ring members.

Also suitable are semicrystalline polyamides (A) that are obtained byreaction of dicarboxylic acids with diamines. Examples of at least onesemicrystalline polyamide (A) that derives from lactam includepolyamides that derive from polycaprolactam, polycaprylolactam and/orpolylaurolactam.

If at least a semicrystalline polyamide (A) obtainable from dicarboxylicacids and diamines is used, dicarboxylic acids used may bealkanedicarboxylic acids having 6 to 12 carbon atoms. Aromaticdicarboxylic acids are also suitable.

Examples of dicarboxylic acids here include adipic acid, azelaic acid,sebacic acid and dodecanedicarboxylic acid.

Examples of suitable diamines include alkanediamines having 4 to 12carbon atoms and aromatic or cyclic diamines, for examplem-xylylenediamine, di(4-aminophenyl)methane,di(4-aminocyclohexyl)methane, 2,2-di(4-aminophenyl)propane or2,2-di(4-aminocyclohexyl)propane.

Preferred components (A) are polycaprolactam (nylon-6) and nylon-6/6,6copolyamide. Nylon-6/6,6 copolyamide preferably has a proportion of 5%to 95% by weight of caprolactam units, based on the total weight of thenylon-6/6,6 copolyamide.

Also suitable as at least one semicrystalline polyamide (P) arepolyamides obtainable by copolymerization of two or more of the monomersmentioned above and below or mixtures of a plurality of polyamides inany desired mixing ratio. Particular preference is given to mixtures ofnylon-6 with other polyamides, especially nylon-6/6,6 copolyamide.

The non-comprehensive list which follows comprises the aforementionedpolyamides and further suitable semicrystalline polyamides (A), and themonomers present.

AB Polymers:

PA 4 pyrrolidone PA 6 ε-caprolactam PA 7 enantholactam PA 8caprylolactam PA 9 9-aminopelargonic acid P 11 11-aminoundecanoic acid P12 laurolactam

AA/BB Polymers:

PA 46 tetramethylenediamine, adipic acid PA 66 hexamethylenediamine,adipic acid PA 69 hexamethylenediamine, azelaic acid PA 610hexamethylenediamine, sebacic acid PA 612 hexamethylenediamine,decanedicarboxylic acid PA 613 hexamethylenediamine,undecanedicarboxylic acid PA 1212 dodecane-1,12-diamine,decanedicarboxylic acid PA 1313 tridecane-1,13-diamine,undecanedicarboxylic acid PA 6T hexamethylenediamine, terephthalic acidPA MXD6 m-xylylenediamine, adipic acid PA 6/66 (see PA 6 and PA 66) PA6/12 (see PA 6 and PA 12) PA 6/6,36 ε-caprolactam, hexamethylenediamine,C₃₆ dimer acid PA 6T/6 (see PA 6T and PA 6)

Preferably, component (A) is selected from the group consisting of PA 4,PA 6, PA 7, PA 8, PA 9, PA 11, PA 12, PA 46, PA 66, PA 69, PA 6.10, PA6.12, PA 6.13, PA 6/6.36, PA 6T/6, PA 12.12, PA 13.13, PA 6T, PA MXD6,PA 6/66, PA 6/12 and copolyamides of these.

The present invention therefore also provides a process in whichcomponent (A) is selected from the group consisting of PA 4, PA 6, PA 7,PA 8, PA 9, PA 11, PA 12, PA 46, PA 66, PA 69, PA 6.10, PA 6.12, PA6.13, PA 6/6.36, PA6T/6, PA 12.12, PA 13.13, PA 6T, PA MXD6, PA 6/66, PA6/12 and copolyamides of these.

Most preferably, component (A) is selected from the group consisting ofnylon-6 and nylon-6/6,6.

Component (B)

Component (B) is at least one amorphous polyamide.

In the context of the present invention “at least one amorphouspolyamide” means either exactly one amorphous polyamide or a mixture oftwo or more amorphous polyamides.

“Amorphous” in the context of the present invention means that thepolyamide does not have any melting point in differential scanningcalorimetry (DSC) measured according to ISO 11357.

“No melting point” means that the enthalpy of fusion of the amorphouspolyamide ΔH2_((B)) is less than 10 J/g, preferably less than 8 J/g andespecially preferably less than 5 J/g, in each case measured by means ofdifferential scanning calorimetry (DSC) according to ISO 11357-4: 2014.

The at least one amorphous polyamide (B) of the invention thus typicallyhas an enthalpy of fusion ΔH2_((B)) of less than 10 J/g, preferably ofless than 8 J/g and especially preferably of less than 5 J/g, in eachcase measured by means of differential scanning calorimetry (DSC)according to ISO 11357-4:2014.

Suitable amorphous polyamides generally have a viscosity number(VN_((B))) in the range from 60 to 200 mL/g, preferably in the rangefrom 70 to 150 mL/g and especially preferably in the range from 75 to125 mL/g, determined in a 0.5% by weight solution of component (B) in96% by weight sulfuric acid at 25° C. to ISO 307:2013-08.

Component (B) of the invention typically has a glass transitiontemperature (T_(G(B))), where the glass transition temperature(T_(G(B))) is typically in the range from 100 to 180° C., preferably inthe range from 110 to 160° C. and especially preferably in the rangefrom 120 to 155° C., determined by means of ISO 11357-2:2014.

Suitable components (B) have a weight-average molecular weight(M_(W(B))) in the range from 5000 to 35 000 g/mol, preferably in therange from 10 000 to 30 000 g/mol and especially preferably in the rangefrom 15 000 to 25 000 g/mol. The weight-average molecular weight isdetermined by means of SEC-MALLS (Size Exclusion ChromatographyMulti-Angle Laser Light Scattering) according to Chi-San Wu, “Handbookof Size Exclusion Chromatography and the Related Techniques”, page 19.

Preferably, component (B) is an amorphous semiaromatic polyamide.Amorphous semiaromatic polyamides of this kind are known to thoseskilled in the art and are selected, for example, from the groupconsisting of PA 6I/6T, PA 6I and PA 6/3T. Component (B) is thereforepreferably selected from the group consisting of PA6I/6T, PA 6I, PA6/3T.

The present invention therefore also provides a process in whichcomponent (B) is selected from the group consisting of PA 6I/6T, PA 6Iand PA 6/3T.

When polyamide 6I/6T is used as component (B), this may comprise anydesired proportions of 6I and 6T structural units. Preferably, the molarratio of 6I structural units to 6T structural units is in the range from1:1 to 3:1, more preferably in the range from 1.5:1 to 2.5:1 andespecially preferably in the range from 1.8:1 to 2.3:1.

The MVR (275° C./5 kg) (melt volume flow rate) of component (B) ispreferably in the range from 50 mL/10 min to 150 mL/10 min, morepreferably in the range from 95 mL/10 min to 105 mL/10 min.

The zero shear rate viscosity η₀ of component (B) is, for example, inthe range from 770 to 3250 Pas. Zero shear rate viscosity η₀ isdetermined with a “DHR-1” rotary viscometer from TA Instruments and aplate-plate geometry with a diameter of 25 mm and a plate separation of1 mm. Unequilibrated samples of component (B) are dried at 80° C. underreduced pressure for 7 days and these are then analyzed with atime-dependent frequency sweep (sequence test) with an angular frequencyrange of 500 to 0.5 rad/s. The following further analysis parameterswere used: deformation: 1.0%, analysis temperature: 240° C., analysistime: 20 min, preheating time after sample preparation: 1.5 min.

Component (B) has an amino end group concentration (AEG) which ispreferably in the range from 30 to 45 mmol/kg and especially preferablyin the range from 35 to 42 mmol/kg.

For determination of the amino end group concentration (AEG), 1 g ofcomponent (B) is dissolved in 30 mL of a phenol/methanol mixture (volumeratio of phenol:methanol 75:25) and then subjected to potentiometrictitration with 0.2 N hydrochloric acid in water.

Component (B) has a carboxyl end group concentration (CEG) which ispreferably in the range from 60 to 155 mmol/kg and especially preferablyin the range from 80 to 135 mmol/kg.

For determination of the carboxyl end group concentration (CEG), 1 g ofcomponent (B) is dissolved in 30 mL of benzyl alcohol. This is followedby visual titration at 120° C. with 0.05 N potassium hydroxide solutionin water.

Component (C)

According to the invention, component (C) is at least one mineral flameretardant.

In the context of the present invention, “at least one mineral flameretardant” means either exactly one mineral flame retardant or a mixtureof two or more mineral flame retardants.

In the context of the present invention, a mineral flame retardant isunderstood to mean a compound that restricts, slows or prevents thespread of fires and is additionally based on minerals.

It will be apparent that component (C) is different than any at leastone reinforcing agent present in the sinter powder (SP). Component (C)is likewise different than any at least one additive present in thesinter powder (SP).

It is additionally preferable that the sinter powder (SP) does notcomprise any mineral flame retardant except for component (C).Especially preferably, the sinter powder (SP) does not comprise anyflame retardant except for component (C).

Preferably, the at least one mineral flame retardant is based onaluminum and/or magnesium.

The present invention therefore also provides a process in whichcomponent (C) is based on magnesium and/or aluminum.

Preference is given to flame retardants that eliminate water at elevatedtemperatures. Therefore, preferred mineral flame retardants are aluminumhydroxide and/or magnesium hydroxide and/or aluminum oxide hydroxide.Magnesium hydroxide is particularly preferred as the at least onemineral flame retardant.

The at least one mineral flame retardant may also be used, for example,as mineral. A suitable mineral is, for example, boehmite. Boehmite hasthe chemical composition AlO(OH) or γ-AlOOH (aluminum oxide hydroxide).

Aluminum hydroxide is also referred to as ATH or aluminum trihydroxide.Magnesium hydroxide is also referred to as MDH or magnesium dihydroxide.

The present invention therefore also provides a process in whichcomponent (C) is selected from the group consisting of magnesiumhydroxide, aluminum oxide hydroxide and aluminum hydroxide.

Component (C) has, for example, a D10 in the range from 0.3 to 1.2 μm, aD50 in the range from 1.2 to 2 μm and a D90 in the range from 2 to 5 μm.

Preferably, component (C) has a D10 in the range from 0.5 to 1 μm, a D50in the range from 1.3 to 1.8 μm and a D90 in the range from 2 to 4 am.

The D10, D50 and D90 values are determined as described above for theD10, D50 and D90 of the sinter powder (SP).

The present invention therefore also provides a process for producing asinter powder (SP) in which component (C) has a D10 in the range from0.3 to 1.2 μm, a D50 in the range from 1.2 to 2 μm and a D90 in therange from 2 to 5 μm.

Component (C) may additionally have been surface-modified. For example,component (C) has been aminosilane-modified.

Step ii)

In step ii), the layer of the sinter powder (SP) provided in step i) isexposed.

On exposure, at least some of the layer of the sinter powder (SP) melts.The molten sinter powder (SP) coalesces and forms a homogeneous melt.After the exposure, the molten part of the layer of the sinter powder(SP) cools down again and the homogeneous melt solidifies again.

Suitable methods of exposure include all methods known to one skilled inthe art. Preferably, the exposure in step ii) is effected with aradiation source. The radiation source is preferably selected from thegroup consisting of infrared sources and lasers. Especially preferredinfrared sources are near infrared sources.

The present invention therefore also provides a process in which theexposing in step ii) is effected with a radiation source selected fromthe group consisting of lasers and infrared sources.

Suitable lasers are known to those skilled in the art and for examplefiber lasers, Nd:YAG lasers (neodymium-doped yttrium aluminum garnetlaser) or carbon dioxide lasers.

If the radiation source used in the exposing in step ii) is a laser, thelayer of the sinter powder (SP) provided in step i) is typically exposedlocally and briefly to the laser beam. This selectively melts just theparts of the sinter powder (SP) that have been exposed to the laserbeam. If a laser is used in step ii), the process of the invention isalso referred to as selective laser sintering. Selective laser sinteringis known per se to those skilled in the art.

If the radiation source used in the exposing in step ii) is an infraredsource, especially a near infrared source, the wavelength at which theradiation source radiates is typically in the range from 780 nm to 1000μm, preferably in the range from 780 nm to 50 am and especially in therange from 780 nm to 2.5 am.

In the exposing in step ii), in that case, the entire layer of thesinter powder (SP) is typically exposed. In order that only the desiredregions of the sinter powder (SP) melt in the exposing, aninfrared-absorbing ink (IR-absorbing ink) is typically applied to theregions that are to melt.

The process for producing the shaped body in that case preferablycomprises, between step i) and step ii), a step i-1) of applying atleast one IR-absorbing ink to at least part of the layer of the sinterpowder (SP) provided in step i).

The present invention therefore also further provides a process forproducing a shaped body, comprising the steps of

-   i) providing a layer of a sinter powder (SP) comprising the    following components:    -   (A) at least one semicrystalline polyamide,    -   (B) at least one amorphous polyamide,    -   (C) at least one mineral flame retardant,-   i-1) applying at least one IR-absorbing ink to at least part of the    layer of the sinter powder (SP) provided in step i),-   ii) exposing the layer of the sinter powder (SP) provided in step    i).

Suitable IR-absorbing inks are all IR-absorbing inks known to the personskilled in the art, especially IR-absorbing inks known to the personskilled in the art for high-speed sintering.

IR-absorbing inks typically comprise at least one absorber that absorbsIR radiation, preferably NIR radiation (near infrared radiation). In theexposing of the layer of the sinter powder (SP) in step ii), theabsorption of the IR radiation, preferably the NIR radiation, by the IRabsorber present in the IR-absorbing inks results in selective heatingof the part of the layer of the sinter powder (SP) to which theIR-absorbing ink has been applied.

The IR-absorbing ink may, as well as the at least one absorber, comprisea carrier liquid. Suitable carrier liquids are known to those skilled inthe art and are, for example, oils or solvents.

The at least one absorber may be dissolved or dispersed in the carrierliquid.

If the exposure in step ii) is effected with a radiation source selectedfrom infrared sources and if step i-1) is conducted, the process of theinvention is also referred to as high-speed sintering (HSS) or multijetfusion process (MJF). These methods are known per se to the personskilled in the art.

After step ii), the layer of the sinter powder (SP) is typically loweredby the layer thickness of the layer of the sinter powder (SP) providedin step i) and a further layer of the sinter powder (SP) is applied.This is subsequently exposed again in step ii).

This firstly bonds the upper layer of the sinter powder (SP) to thelower layer of the sinter powder (SP); in addition, the particles of thesinter powder (SP) within the upper layer are bonded to one another byfusion.

In the process of the invention, steps i) and ii) and optionally i-1)can thus be repeated.

By repeating the lowering of the powder bed, the applying of the sinterpowder (SP) and the exposure and hence the melting of the sinter powder(SP), three-dimensional shaped bodies are produced. It is possible toproduce shaped bodies that also have cavities, for example. Noadditional support material is necessary since the unmolten sinterpowder (SP) itself acts as a support material.

The present invention therefore also further provides a shaped bodyobtainable by the process of the invention.

Of particular significance in the process of the invention is themelting range of the sinter powder (SP), called the sintering window(W_(SP)) of the sinter powder (SP).

The sintering window (W_(SP)) of the sinter powder (SP) can bedetermined by differential scanning calorimetry (DSC) for example.

In differential scanning calorimetry, the temperature of a sample, i.e.in the present case a sample of the sinter powder (SP), and thetemperature of a reference are altered linearly over time. For thispurpose, heat is supplied to/removed from the sample and the reference.The amount of heat Q necessary to keep the sample at the sametemperature as the reference is determined. The amount of heat Q_(R)supplied to/removed from the reference serves as a reference value.

If the sample undergoes an endothermic phase transformation, anadditional amount of heat Q must be supplied to maintain the sample atthe same temperature as the reference. If an exothermic phasetransformation takes place, an amount of heat Q has to be removed tokeep the sample at the same temperature as the reference. Themeasurement affords a DSC diagram in which the amount of heat Q suppliedto/removed from the sample is plotted as a function of temperature T.

Measurement typically involves initially performing a heating run (H),i.e. the sample and the reference are heated in a linear manner. Duringthe melting of the sample (solid/liquid phase transformation), anadditional amount of heat Q has to be supplied to keep the sample at thesame temperature as the reference. In the DSC diagram a peak known asthe melting peak is then observed.

After the heating run (H), a cooling run (C) is typically measured. Thisinvolves cooling the sample and the reference linearly, i.e. heat isremoved from the sample and the reference. During thecrystallization/solidification of the sample (liquid/solid phasetransformation), a greater amount of heat Q has to be removed to keepthe sample at the same temperature as the reference, since heat isliberated in the course of crystallization/solidification. In the DSCdiagram of the cooling run (C), a peak, called the crystallization peak,is then observed in the opposite direction from the melting peak.

In the context of the present invention, the heating during the heatingrun is typically effected at a heating rate of 20 K/min. The coolingduring the cooling run in the context of the present invention istypically effected at a cooling rate of 20 K/min.

A DSC diagram comprising a heating run (H) and a cooling run (C) isdepicted by way of example in FIG. 1. The DSC diagram can be used todetermine the onset temperature of melting (T_(M) ^(onset)) and theonset temperature of crystallization (T_(C) ^(onset)).

To determine the onset temperature of melting (T_(M) ^(onset)), atangent is drawn against the baseline of the heating run (H) at thetemperatures below the melting peak. A second tangent is drawn againstthe first point of inflection of the melting peak at temperatures belowthe temperature at the maximum of the melting peak. The two tangents areextrapolated until they intersect. The vertical extrapolation of theintersection to the temperature axis denotes the onset temperature ofmelting (T_(M) ^(onset)).

To determine the onset temperature of crystallization (T_(C) ^(onset)),a tangent is drawn against the baseline of the cooling run (C) at thetemperatures above the crystallization peak. A second tangent is drawnagainst the point of inflection of the crystallization peak attemperatures above the temperature at the minimum of the crystallizationpeak. The two tangents are extrapolated until they intersect. Thevertical extrapolation of the intersection to the temperature axisindicates the onset temperature of crystallization (T_(C) ^(onset)).

The sintering window (W) results from the difference between the onsettemperature of melting (T_(M) ^(onset)) and the onset temperature ofcrystallization (T_(C) ^(onset)). Thus:

W=T _(M) ^(onset) −T _(C) ^(onset).

In the context of the present invention, the terms “sintering window(W_(SP))”, “size of the sintering window (W_(SP))” and “differencebetween the onset temperature of melting (T_(M) ^(onset)) and the onsettemperature of crystallization (T_(C) ^(onset))” have the same meaningand are used synonymously.

The sinter powder (SP) of the invention is of particularly goodsuitability for use in a sintering process.

The present invention therefore also provides for the use of a sinterpowder (SP) comprising the following components:

(A) at least one semicrystalline polyamide,

(B) at least one amorphous polyamide,

(C) at least one mineral flame retardant,

in a sintering process.

Shaped Body

The process of the invention affords a shaped body. The shaped body canbe removed from the powder bed directly after the solidification of thesinter powder (SP) molten on exposure in step ii). It is likewisepossible first to cool the shaped body and only then to remove it fromthe powder bed. Any adhering particles of the sinter powder that havenot been melted can be mechanically removed from the surface by knownmethods.

Methods for surface treatment of the shaped body include, for example,vibratory grinding or barrel polishing, and also sandblasting, glassbead blasting or microbead blasting.

It is also possible to subject the shaped bodies obtained to furtherprocessing or, for example, to treat the surface.

The present invention therefore further provides a shaped bodyobtainable by the process of the invention.

The shaped bodies obtained typically comprise in the range from 30% to70% by weight of component (A), in the range from 5% to 25% by weight ofcomponent (B) and in the range from 20% to 60% by weight of component(C), based in each case on the total weight of the shaped body.

Preferably, the shaped body comprises in the range from 40% to 70% byweight of component (A), in the range from 7% to 23% by weight ofcomponent (B) and in the range from 22% to 45% by weight of component(C), based in each case on the total weight of the shaped body.

Most preferably, the shaped body comprises in the range from 50% to 65%by weight of component (A), in the range from 10% to 20% by weight ofcomponent (B) and in the range from 25% to 35% by weight of component(C), based in each case on the total weight of the shaped body.

According to the invention, component (A) is the component (A) that waspresent in the sinter powder (SP). Component (B) is likewise thecomponent (B) that was present in the sinter powder (SP), and component(C) is likewise the component (C) that was present in the sinter powder(SP).

If the sinter powder (SP) comprises the at least one additive and/or theat least one reinforcing agent, the shaped body obtained in accordancewith the invention typically also comprises the at least one additiveand/or the at least one reinforcing agent.

If step i-1) has been conducted, the shaped body additionally typicallycomprises the IR-absorbing ink.

It will be clear to the person skilled in the art that, as a result ofthe exposure of the sinter powder (SP), components (A), (B) and (C) andany at least one additive and the at least one reinforcing agent canenter into chemical reactions and be altered as a result. Such reactionsare known to those skilled in the art.

Preferably, components (A), (B) and (C) and any at least one additiveand the at least one reinforcing agent do not enter into any chemicalreaction on exposure in step ii); instead, the sinter powder (SP) merelymelts.

The invention is elucidated in detail hereinafter by examples, withoutrestricting it thereto.

EXAMPLES

The following components are used:

-   -   semicrystalline polyamide (component (A)):    -   (P1) nylon-6 (Ultramid B27, BASF SE)    -   (P2) nylon-6/6,6 (Ultramid C33, BASF SE)    -   amorphous polyamide (component (B)):    -   (AP1) nylon-6I/6T (Grivory G16, EMS), with a molar ratio of        6I:6T of 1.9:1    -   (AP2) nylon-6/3T (Trogamid T 5000, Evonik)    -   mineral flame retardant (component (C)):    -   (FM1) magnesium hydroxide (Magnifin H5 IV, Albemarle),        aminosilane-modified, bulk density 501 kg/m³, particle size        distribution D10=0.8 μm, D50=1.7 μm, D90=3.1 μm, determined by        means of laser scattering    -   Additive:    -   (A1) phenolic antioxidant (Irganox 1098        (N,N′-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide))),        BASF SE)    -   (A2) carbon black in the form of batch UB420 (30% in PA 6),        (Special black 4, CAS No. 1333-86-4, Evonik)

Table 1 states the essential parameters of the semicrystallinepolyamides used (component (A)).

Table 2 the essential parameters of the amorphous polyamides used(component (B)).

TABLE 1 Zero-shear viscosity η₀ at AEG CEG T_(M) T_(G) 240° C. Type[mmol/kg] [mmol/kg] [° C.] [° C.] [Pas] P1 PA 6 36 54 220.0 53 399 P2 PA6/66 47 40 193.7 50 2300

TABLE 2 Zero-shear viscosity η₀ at AEG CEG 240° C. Type [mmol/kg][mmol/kg] T_(g), [° C.] [Pas] AP1 PA 6I6T 37 86 125 770 AP2 PA 6/3T 4559 150 7200 at 0.5 rad/s

AEG indicates the amino end group concentration. This is determined bymeans of titration. For determination of the amino end groupconcentration (AEG), 1 g of the component (semicrystalline polyamide oramorphous polyamide) is dissolved in 30 mL of a phenol/methanol mixture(volume ratio of phenol:methanol 75:25) and then subjected to visualtitration with 0.2 N hydrochloric acid in water.

CEG indicates the carboxyl end group concentration. This is determinedby means of titration. For determination of the carboxyl end groupconcentration (CEG), 1 g of the component (semicrystalline polyamide oramorphous polyamide) is dissolved in 30 mL of benzyl alcohol and thensubjected to visual titration at 120° C. with 0.05 N potassium hydroxidesolution in water.

The melting temperature (T_(M)) of the semicrystalline polyamides andall glass transition temperatures (T_(G)) were each determined by meansof differential scanning calorimetry.

For determination of the melting temperature (T_(M)), as describedabove, a first heating run (H1) at a heating rate of 20 K/min wasmeasured. The melting temperature (T_(M)) then corresponded to thetemperature at the maximum of the melting peak of the first heating run(H1).

For determination of the glass transition temperature (T_(G)), after thefirst heating run (H1), a cooling run (C) and subsequently a secondheating run (H2) were measured. The cooling run was measured at acooling rate of 20 K/min. The first heating run (H1) and the secondheating run (H2) were measured at a heating rate of 20 K/min. The glasstransition temperature (T_(G)) was then determined at half the stepheight of the second heating run (H2).

The zero shear rate viscosity no was determined with a “DHR-1” rotaryviscometer from TA Instruments and a plate-plate geometry with adiameter of 25 mm and a plate separation of 1 mm. Unequilibrated sampleswere dried at 80° C. under reduced pressure for 7 days and these werethen analyzed with a time-dependent frequency sweep (sequence test) withan angular frequency range of 500 to 0.5 rad/s. The following furtheranalysis parameters were used: deformation: 1.0%, analysis temperature:240° C., analysis time: 20 min, preheating time after samplepreparation: 1.5 min.

Production of Sinter Powders in a Twin-Screw Extruder

For production of sinter powders, the components specified in table 3were compounded in the ratio specified in table 3 in a twin-screwextruder (ZE25) at a speed of 230 rpm (revolutions per minute) at 270°C. at a throughput of 20 kg/h, pelletized, and then processed with aliquid nitrogen-cooled pinned-disk mill to give powders (particle sizedistribution 10 to 100 μm).

TABLE 3 (P1) (P2) (AP1) (AP2) (FM1) (A1) (A2) Example [% by wt.] [% bywt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] [% by wt.] V1 78.6 210.4 B2 66.8 17.8 15 0.4 B3 62.8 16.8 20 0.4 V4 79.6 20 0.4 B4a 64.3610.0 25 0.4 0.25 B4b 64.25 10.5 25 0.25 B5 56.5 15.1 28 0.4 B6 56.1715.1 28 0.4 0.33 B7 56.17 15.1 28 0.4 0.33 B8 51.0 13.6 35 0.4 B9 55.659.1 35 0.25 B10 39.1 10.5 50 0.4

For the powders, the melting temperature (T_(M)) was determined asdescribed above.

The crystallization temperature (T_(C)) was determined by means ofdifferential scanning calorimetry (DSC). For this purpose, first aheating run (H) at a heating rate of 20 K/min and then a cooling run (C)at a cooling rate of 20 K/min were measured. The crystallizationtemperature (T_(C)) is the temperature at the extreme of thecrystallization peak.

The magnitude of the complex shear viscosity was determined by means ofa plate-plate rotary rheometer at an angular frequency of 0.5 rad/s anda temperature of 240° C. A “DHR-1” rotary viscometer from TA Instrumentswas used, with a diameter of 25 mm and a plate separation of 1 mm.Unequilibrated samples were dried at 80° C. under reduced pressure for 7days and these were then analyzed with a time-dependent frequency sweep(sequence test) with an angular frequency range of 500 to 0.5 rad/s. Thefollowing further analysis parameters were used: deformation: 1.0%,analysis time: 20 min, preheating time after sample preparation: 1.5min.

The sintering window (W) was determined, as described above, as thedifference between the onset temperature of melting (T_(M) ^(onset)) andthe onset temperature of crystallization (T_(C) ^(onset)).

To determine the thermooxidative stability of the sinter powders, thecomplex shear viscosity of freshly produced sinter powders and of sinterpowders after oven aging at 0.5% oxygen and 195° C. for 16 hours wasdetermined. The ratio of viscosity after storage (after aging) to theviscosity before storage (before aging) was determined.

The viscosity is measured by means of rotary rheology at a measurementfrequency of 0.5 rad/s at a temperature of 240° C.

The results can be seen in table 4.

TABLE 4 Magnitude of complex Ratio of viscosity Sintering viscosity at0.5 after aging to Sintering window W Example rad/s, 240° C. [Pas]before aging T_(M) [° C.] T_(C) [° C.] window W[K] after aging [K] V1632 3.4 218.2 172.5 28.3 27.1 B2 1030 0.98 217.6 173.8 24.4 24.0 B3 13501.24 217.9 174.9 26.1 25.9 V4 1140 0.95 219.1 183.7 21.6 17.5 B4a 13801.26 217.8 178.8 22.1 n.d. B4b 6250 3.8 193.0 143.2 29.6 n.d. B5 16461.2 217.6 173.8 26.4 n.d. B6 1630 1.2 217.2 173.0 26.3 25.7 B7 2910 1.05218.2 176.0 25.3 21.1 B8 2646 1.5 217.3 173.3 24.6 n.d. B9 9300 5.5192.5 143.9 29.0 40.1 B10 6100 5.3 217.1 172.6 27.9 n.d. n.d.: notdetermined

It is apparent that the sinter powders of the invention have a sinteringwindow sufficient for selective laser sintering, even after aging.

In addition, for the sinter powders obtained, bulk density is determinedto DIN EN ISO 60 and tamped density to DIN EN ISO 787-11, as is theHausner factor as the ratio of tamped density to bulk density.

Particle size distribution, reported as the D10, D50 and D90 value, wasdetermined as described above with a Malvern Mastersizer.

Magnesium content was determined by means of atomic spectroscopy.

The avalanche angle was determined by means of a Revolution PowderAnalyzer (RPA) with a rotation speed of 0.6 rpm and 15 images persecond. The average was found from 128 avalanche events.

The results can be seen in table 5.

TABLE 5 Bulk density Tamped density Hausner D10 D50 D90 Avalanche Mgcontent Examples [kg/m³] [kg/m³] factor [μm] [μm] [μm] angle [°] [g/100g] V1 460 570 1.24 39 65 107 52   0   B2 499 600 1.20 42 66.5 104 n.d.n.d. B3 532 642 1.21 37 63.5 104 n.d. 8.5 V4 n.d. n.d. n.d. 38 65.5 108n.d. n.d. B4a n.d. n.d. n.d. 39.2 65.3 106 n.d. n.d. B4b 520 634 1.22 3965.8 108 n.d. n.d. B5 n.d. n.d. n.d. 35 63.5 108 45.9 n.d. B6 n.d. n.d.n.d. 48.5 75.7 117 51.1 n.d. B7 n.d. n.d. n.d. 43 67.4 104 n.d. n.d. B8n.d. n.d. n.d. 38 63 103 n.d. n.d. B9 553 684 1.24 37.6 64.5 107 n.d.n.d. B10 n.d. n.d. n.d. 40 66 107 n.d. n.d. n.d.: not determined

Laser Sintering Experiments

The sinter powders (SP) were introduced with a layer thickness of 0.1 mminto the cavity at the temperature specified in table 6. The sinterpowders were subsequently exposed to a laser with the laser power outputspecified in table 6 and the point spacing specified, with a speed ofthe laser over the sample during exposure of 15 m/sec. The point spacingis also known as laser spacing or lane spacing. Selective lasersintering typically involves scanning in stripes. The point spacinggives the distance between the centers of the stripes, i.e. between thetwo centers of the laser beam for two stripes. The laser sinteringexperiments were done on Farsoon HT251.

TABLE 6 Construction space temperature Laser power Laser Point Example[° C.] output [W] speed [m/s] spacing [mm] V1 198 25 5 0.2 B2 206 55 150.2 B3 205 32 5 0.2 V4 203 68 12.5 0.2 B4a 207 50 15 0.2 B4b 184 50 150.2 B5 208 55 15 0.2 B6 202 55 15 0.2 B7 204 55 15 0.2 B8 200 32 5 0.2B9 190 55 15 0.2 B10 206 30 5 0.2

The flame retardancy properties of the laser-sintered test specimenswere determined to UL 94 Vx: 2016 (vertical test). The determination waseffected firstly after storage at 23° C. and 50% relative humidity for 2days and secondly after storage at 70° C. in a drying cabinet for 7days.

The results and the thickness of the test specimens are shown in table7.

TABLE 7 Thickness of UL test 2 days/23° C./ Example specimen [mm] 50%r.h. 7 days/70° C. V1 0.8 V-- V-- 1.7 V-- V-- B2 0.96 V-- V-- 1.6 V--V-- B3 1.25-1.4 V-2, 41 s V-2, 40 s 0.85 V-2, 20 s V-2, 17 s 0.94 V-2,66 s n.d. 1.5 V-2, 44 s V-2, 48 s 2.2 V-2, 51 s V-2, 69 s V4 0.84 V-2,15 s V-2, 69 s 1.7 V-2, 49 s V-2, 73 s B4a 0.52 V-2, 14 s V-2, 9 s 0.84V-2, 9 s V-2, 21 s 1.7 V-2, 60 s V-2, 68 s B4b 0.82 V-2, 16 s V-2, 6 s1.56 V-2 38 s V-2, 31 s B5 1.0 n.d. V-2, 33 s 1.8 n.d. V-2, 79 s B6 0.81V-2, 13 s V-2, 11 s 1.6 V-2, 44 s V-2, 46 s B7 0.88 V-2, 12 s V-2, 19 s1.6 V-2, 47 s V-2, 57 s B8 0.84 V-2, 17 s n.d. 1.8 V-2, 54 s n.d. B90.95 V-2, 19 s V-2, 13 s 1.7 V-2, 48 s V-2, 42 s B10 1.0 V-2, 21 s n.d.1.9 V-2, 19 s n.d. n.d.: not determined

Subsequently. the properties of the tensile bars (sinter bars) obtainedwere additionally determined. The tensile bars (sinter bars) obtainedwere tested in the dry state after drying at 80° C. for 336 hours underreduced pressure. The results are shown in table 8. Charpy specimenswere also produced. which were likewise tested in dry form (to ISO179-2/1 eA(F): 1997+Amd. 1: 2011 and to ISO 179-2/1 eU: 1997+Amd. 1:2011).

Tensile strength, tensile modulus of elasticity and elongation at breakwere determined to ISO 527-2: 2012.

Heat deflection temperature (HDT) was determined according to ISO 75-2:2013. using both Method A with an edge fiber stress of 1.8 N/mm² andMethod B with an edge fiber stress of 0.45 N/mm².

The results can be seen in table 8.

TABLE 8 Charpy Charpy impact impact Tensile resistance resistanceTensile modulus of Elongation unnotched notched strength elasticity atbreak HDT A HDT B Example [kJ/m²] [kJ/m²] [MPa] [MPa] [%] [° C.] [° C.]V1  4.94 1.5   56.7 3660 1.7   94.4   150.4 B2 n.d. n.d. n.d. n.d. n.d.n.d. n.d. B3 7.3 2.9 61 4390 1.6 114 210 V4 8.2 2.3 62 4370 1.8 n.d.n.d. B4a 7.0 1.5 63 5170 1.4 n.d. n.d. B4b n.d. n.d. 54 3610 1.9 n.d.n.d. B5 8.1 1.4 64 5230 1.4 116 203 B6 n.d. n.d. 49 5560 1.6 123 203 B7n.d. n.d. 57 4780 1.4 n.d. n.d. B8 n.d. n.d. n.d. n.d. n.d. n.d. n.d. B9n.d. n.d. 41 3680 1.5 n.d. n.d. B10 5.0 2.0 53 7090 0.8 126 204 n.d.:not determined

The sinter powders of the invention show good SLS processability and lowwarpage.

1. A process for producing a shaped body, comprising the steps of: i)providing a layer of a sinter powder (SP) comprising the followingcomponents: (A) at least one semicrystalline polyamide, (B) at least oneamorphous polyamide, (C) at least one mineral flame retardant, ii)exposing the layer of the sinter powder (SP) provided in step i).
 2. Theprocess according to claim 1, wherein component (C) is based onmagnesium and/or aluminum.
 3. The process according to claim 1 or 2,wherein component (C) is selected from the group consisting of magnesiumhydroxide, aluminum oxide hydroxide and aluminum hydroxide.
 4. Theprocess according to any of claims 1 to 3, wherein the exposing in stepii) is effected with a radiation source selected from the groupconsisting of lasers and infrared sources.
 5. The process according toany of claims 1 to 4, wherein the sinter powder (SP) comprises in therange from 30% to 70% by weight of component (A), in the range from 5%to 25% by weight of component (B) and in the range from 20% to 60% byweight of component (C), based in each case on the total weight of thesinter powder (SP).
 6. The process according to any of claims 1 to 5,wherein component (A) is selected from the group consisting of PA 4, PA6, PA 7, PA 8, PA 9, PA 11, PA 12, PA 46, PA 66, PA 69, PA 6.10, PA6.12, PA 6.13, PA 6/6.36, PA6T/6, PA 12.12, PA 13.13, PA 6T, PA MXD6, PA6/66, PA 6/12 and copolyamides of these.
 7. The process according to anyof claims 1 to 6, wherein component (B) is selected from the groupconsisting of PA 6I/6T, PA 6I and PA 6/3T.
 8. The process according toany of claims 1 to 7, wherein the sinter powder (SP) additionallycomprises in the range from 0.1% to 10% by weight of at least oneadditive selected from the group consisting of antinucleating agents,stabilizers, end group functionalizers, dyes and color pigments, basedon the total weight of the sinter powder (SP).
 9. The process accordingto any of claims 1 to 8, wherein component (C) in the sinter powder (SP)has been coated with component (A) and/or with component (B).
 10. Theprocess according to any of claims 1 to 9, wherein the sinter powder(SP) has a D10 in the range from 10 to 60 μm, a D50 in the range from 25to 90 μm and a D90 in the range from 50 to 150 μm.
 11. A process forproducing a sinter powder (SP), comprising the steps of a) mixing thefollowing components: (A) at least one semicrystalline polyamide, (B) atleast one amorphous polyamide, (C) at least one mineral flame retardant,b) grinding the mixture obtained in step a) to obtain the sinter powder(SP).
 12. The process according to claim 11, wherein component (C) has aD10 in the range from 0.3 to 1.2 μm, a D50 in the range from 1.2 to 2 μmand a D90 in the range from 2 to 5 μm.
 13. A sinter powder (SP)obtainable by a process according to claim 11 or
 12. 14. The use of asinter powder (SP) comprising the following components: (A) at least onesemicrystalline polyamide, (B) at least one amorphous polyamide, (C) atleast one mineral flame retardant, in a sintering process.
 15. A shapedbody obtainable by a process according to any of claims 1 to 10.